1. Field of the Invention
The invention relates to a dental handpiece with a turbine rotor positioned in the head of the handpiece and driving in rotation the rotor spindle and thus also a tool. The turbine rotor is supported on a side of the rotor facing away from the tool and on a side facing the tool, preferably in roller bearings. The handpiece has a drive air channel for the drive air of the turbine and a return channel for the expanded return air of the turbine.
2. Description of the Related Art
Such handpieces have been known for a long time and have been successfully used in practice.
However, a system-inherent disadvantage of such handpieces is that upon ending a work process in the mouth of a patient, when the drive air is interrupted by actuating a corresponding valve in the handpiece control, the turbine will continue to run because of its inertia. This creates an overpressure at the external side of the turbine rotor and a vacuum in the vicinity of its axis.
Since the channel for the return air opens into the turbine chamber in the external area of the rotor, the air is conveyed by the coasting rotor into the return channel, and in the vicinity of the axis air is sucked in through all of the fine channels and gaps within the handpiece. This means that especially air that is contaminated with saliva and blood of the patient currently being treated is sucked into the handpiece and can penetrate through the bearings into the turbine chamber and into the return air channel.
When the handpiece is again switched on, the air that remained in the area of the turbine chamber and the bearings and contaminants that have settled there are now not only removed through the return air channel by the overpressure generated in the entire turbine chamber but a certain amount is also expelled or blown out to the exterior of the handpiece into the mouth, the saliva, and possibly also into an already open wound of the next patient to be treated.
A solution to this problem is disclosed in patent document AT 403 882 B. In this document it is suggested to provide an axial connection between the turbine and the end of the tool holder facing the tool between an area close to the axis and the return channel so that the turbine, which is coasting after being turned off, moves the air in the way of a flow-technological short-circuit within the head of the handpiece but does not suck in air.
In a variant it is suggested to provide a connecting channel at the side of the rotor facing away from the tool between the return air channel and an opening in the vicinity of the axis of the turbine chamber and/or a hollow space in the area of the actuating element for the tool holder.
When designing a practical embodiment of this variant, one is faced with the problem that because of the miniaturization of the head of the handpiece there is no room or only minimal room available for such a connecting channel.